1. Field of the Invention
The present invention relates to mobile communication systems, and more particularly to a method and an apparatus for periodically reporting the buffer status in a mobile communication system.
2. Description of the Related Art
As generally known in the art, the LTE (Long Term Evolution), which is the evolved mobile communication system of the third-generation mobile communication system of UMTS (Universal Mobile Telecommunication Service), provides a high-speed packet service based on the OFDM. In the case of a mobile communication system in which the Node B dynamically allocates a transmission resource, such as LTE or EUDCH (Enhanced Uplink Dedicate Channel), the UE must report the buffer status to the Node B prior to transmitting data through the uplink. Schemes for reporting the buffer status include an event-triggered scheme in which a buffer status report message is transmitted if a specific condition is satisfied, and a periodic scheme in which a buffer status report message is transmitted at a predetermined cycle.
In the case of the EUDCH, both the event-triggered scheme and the periodic scheme have been adopted. Both schemes are also expected to be employed by the LTE.
FIG. 1 shows an exemplary scheme for periodically reporting the buffer status according to the prior art.
When such a periodic scheme is employed, the UE activates a timer after completing the transmission of a buffer status report message. If the timer expires, the UE transmits a new buffer status report message.
Referring to FIG. 1, if no transmission resource has been allocated to the UE 105 when the timer has expired (115), the UE 105 transmits a signal for a scheduling request, for example, to the Node B 110 (120), which then is allocated a transmission resource for the buffer status report (125). The UE 105 then transmits a buffer status report message based on the allocated transmission resource (130).
On the other hand, if the UE 105 has a transmission resource allocated thereto when the timer has expired (135), the UE 105 piggybacks the buffer status report message onto the uplink data by using the allocated transmission resource, and transmits it.
In other words, if the UE is to transmit a buffer status report message with no transmission resource allocated thereto, the UE must transmit a separate uplink signal to the Node B (120), and receive a downlink transmission resource allocation signal from the Node B (125). If a transmission resource has been allocated (135), the UE can directly piggyback and transmit an uplink signal, which includes a buffer status report message, without exchanging a separate control message for transmitting the buffer status report message (140). As such, the buffer status report message is preferably transmitted after a transmission resource has been allocated.